The present description relates to an internal combustion engine, more particularly relates to a method of stopping an internal combustion engine with suppressed vibration during engine stopping.
There is shown and presented, for example in Japanese patent application publication no. 2004-308570A, a method of stopping an engine of a hybrid electric vehicle. Generally, the hybrid electric vehicle more frequently stops and restarts the engine, and therefore, when stopping the engine, it requires smoother engine stop operation. Particularly, the method of '570 publication seeks suppression of a vibration caused by compression of air in the combustion chamber just before the complete stop of the engine rotation. When an engine stop request is issued, fuel is shut off to the combustion chamber, and an electric machine drives the engine with advanced intake valve timing in order to purge air in a surge tank of the engine and keep an engine speed. When the pressure in the surge tank is sufficiently reduced, it is stopped to keep the engine speed, and the intake valve timing is retarded in order to reduce an effective compression ratio by reducing air charge in the combustion chamber with the retarded intake valve timing.
Therefore, at the second stage of the motoring the engine, the reduced effective compression ratio may suppress the vibration caused by the compression of air. However, according to the prior art method, it may take substantial period of time to purge the air in the combustion chamber and electric energy to operate the electric machine to keep the engine speed during the first stage. Therefore, there is a need to improve the method of stopping the internal combustion engine of the prior art.